Conventionally, various image display devices such as a home television set have been adopted in AV devices and OA devices. Such an image display device includes, for example, a CRT (Cathode Ray Tube), a liquid crystal display device, a plasma display device (Plasma Display Panel), an EL (electroliminescent) display device, an LED (Light Emitting Diode) display device, and other types of devices.
In recent years, there has been a demand for making these image display devices lighter, thinner, less power consuming, and finer, and making the display larger. To this date, many display devices meeting such a demand have been developed, and some of them have already been used in actual application.
Of various display devices as mentioned above, the liquid crystal display device has such advantages in that, compared with other display devices, the thickness (depth) is far thinner, the power consumption is low, and a full color can be realized with ease. For this reason, the liquid crystal display device has been used in a variety of fields in various ways, and is considered to be the best candidate for realizing a larger screen.
However, in order to realize a liquid crystal display device with a larger screen, the following problem must be overcome. That is, in the liquid crystal display device, when the screen is made larger, the fraction defective is abruptly increased due to breakage of a signal wire and a pixel failure in the manufacturing process. This inevitably raises the price of the liquid crystal display device.
In order to solve this problem and to realize a larger screen, a variety of liquid crystal display devices of the multi-panel system have been suggested. In the liquid crystal display devices of the multi-panel system, a plurality of liquid crystal panels are connected to one another so as to constitute a single liquid crystal display device.
However, in the liquid crystal display devices of the multi-panel system, the connected portion between liquid crystal panels, namely, a "seam" between liquid crystal panels becomes noticeable on the display. This is caused by the light from the backlight leaking through a gap at the connected portion between liquid crystal panels. Thus, in order to realize a liquid crystal display device capable of natural displaying on a large screen, a technique for disguising the seam is needed.
In order to realize such technique, the applicants of the present invention have suggested a liquid crystal display device adopting a new type of the multi-panel system in Japanese Unexamined Patent publication No. 122769/1996 (Tokukaihei 8-122769). FIG. 11 is a cross sectional view which schematically shows, as such a liquid crystal display device, the arrangement of a liquid crystal display device 101.
As shown in FIG. 11, the liquid crystal display device 101 is provided with a plurality of liquid crystal panels 102 of the active matrix type. In the following, for simplicity, explanations will be given through the case where the number of liquid crystal panel 102 of the liquid crystal display device is two.
A liquid crystal panel 102 has an arrangement wherein a TFT substrate 103 and a CF substrate 104 are combined with each other by a sealant 105, and liquid crystal 106 is enclosed therebetween. The liquid crystal panels 102 are connected adjacent to each other by an adhesive 108 to a large reinforcing substrate 107 having substantially the same refractive index as that of glass from which the TFT substrate 103 and the CF substrate 104 are made.
On substantially the entire surface of the outer side of the reinforcing substrate 107, a polarizing plate (polarizer) 109 is provided. Also, on substantially the entire surface of the outer side of the liquid crystal panels 102, a polarizing plate (polarizer) 110 is provided. The polarization axes of the polarizing plates 109 and 110 are orthogonal to each other.
In the described arrangement, leakage of light from the gap between the liquid crystal panels 102 is prevented by the polarizing plates 109 and 110 which are in the Cross Nicole state. However, in the case of adopting, as the adhesive 108 which binds the edge surfaces of the liquid crystal panels 102, adhesive resin, etc., having birefringence, there is a case where the transmitted light from the backlight, which is determined by the polarizing plates 109 and 110, is modulated by the adhesive 108. As a result, even when the polarizing plates 109 and 110 are in the Cross Nicole state, there is a case that the light from the backlight is transmitted through a connected portion 112 of the liquid crystal panels 102, and partial leakage of light is caused.
As a countermeasure, as shown in FIG. 11, FIG. 12, and FIG. 13, on predetermined positions on the edge surfaces of the liquid crystal panels 102 which are connected adjacent to each other, light-shields 51a and 51b, each having a predetermined height (length in a direction perpendicular with respect to the edge surface) are provided, respectively. As shown in FIG. 13, when connecting the edge surfaces of the liquid crystal panels 102, the light-shields 51a and 51b are connected to each other so as to form a light shielding film, filling the gap between the liquid crystal panels 102. With this arrangement, light passing through the connected portion can be blocked by the light shielding film 51, thus preventing leakage of light from the connected portion 112.
Note that, the light-shields 51a and 51b are also known as a side-black, and are made of, for example, a black silicon rubber. The side-black may be provided, as above, on each edge surface of the liquid crystal panels 102, or may be provided on only one of the edge surfaces. Also, the predetermined position where the side-black is to be provided is a position which does not prevent light from passing through display pixels adjacent to the connected portion 112 between the liquid crystal panels 102, and in this case, a substantially central portion on each edge surface of the liquid crystal panels 102 in a direction of the panel thickness. Since detailed explanation of such predetermined position is discussed in the above-mentioned publication, a further explanation thereof is omitted here.
Despite the described advantage, the arrangement of the liquid crystal display device 101 presents the following problems.
For example, in the case of making a 40 inch (approximately 80 cm.times.60 cm) multi-panel liquid crystal display device 101 by connecting two 29 inch (approximately 40 cm.times.60 cm) liquid crystal panels 102, the length in the lengthwise direction on the edge surfaces of the liquid crystal panels 102 at the connected portion 112 becomes substantially 60 cm, and a side-black having a height of substantially 30 .mu.m is formed on each of the edge surfaces along the length of substantially 60 cm.
FIG. 14 is an explanatory drawing which shows how the glass substrate is cut by a dicing process using a diamond blade. As shown in FIG. 14, when a liquid crystal panel, made of the glass substrate, having a thickness of substantially 2 mm is cut along the cutting line of substantially 60 cm, the cutting edge surface takes the shape of X-Z plane in FIG. 14, with a profile irregularity of substantially 20 .mu.m to 30 .mu.m. Note that, here, the profile irregularity is the distance between the crest and the trough of the waviness on the cutting edge surface of the substrate in Y direction.
Possible reasons for the profile irregularity in the above range are 1 reduced mechanical accuracy of a dicing device as a result of adopting a large dicing device in accordance with the work size (size of glass substrate to be cut) and 2 wobbling blade rotating at a high speed as a result of increased processing speed in accordance with a cutting distance of substantially 60 cm.
When the liquid crystal panels 102 having such a profile irregularity is connected adjacent to each other, as shown in FIG. 15, there is a case that convex portions 102a or concave portions 102b of the cutting edge surfaces make a contact with each other. In such a case, while a gap 113 at the connected portion 112 where the convex portions 102a make a contact with each other is completely sealed by the side-black, at the portion where the concave portions 102b make a contact with each other, the gap 113 is not completely sealed by the side-black.
The following describes the reason for this. Namely, in the arrangement of the liquid crystal display device 101, as shown in FIG. 13, the apices of the light-shields 51a and 51b, which are side-black provided on the liquid crystal panels 102, make a contact with each other. For this reason, the gap between the liquid crystal panels 102 cannot be made narrower than the portion where the convex portions 102a on the edge surfaces are adjacent to each other. As a result, at the portion where the concave portions 102b are adjacent to each other, the gap 113 between the liquid crystal panels 102 is not sealed by the side-black provided on each of the concave portions 102b.
When the gap 113 is present, in the arrangement of the conventional liquid crystal display device 101, even when the polarizing plates 109 and 110 (see FIG. 11) are in the Cross Nicole state, leakage of light is caused through the gap 113.
As means to solve this problem, for example, a method in which the cutting edge surface of the liquid crystal panel 102 prepared by dicing process is smoothed so as to obtain a profile irregularity in an order of several .mu.m. However, this method adds the number of manufacturing steps and lowers operativity, and therefore is not preferable.